The present disclosure relates to actuator drivers, and more particularly to fully digitally controlled actuator drivers.
Actuator drivers are widely used in various products. For example, in optical disk devices, an actuator driver is used for controlling the tilt direction, the tracking direction, and the focus direction of an optical pick-up device, controlling a sled motor which shifts the optical pick-up device in the disk radial direction, controlling a loading motor for taking an optical disk in and out, and controlling a spindle motor for rotary driving an optical disk.
In general, actuator drivers detect a current flowing through a load using a sense resistor, and feed back a detection signal to perform phase compensation of a torque command signal, thereby PWM-driving the load. Almost all phase compensation filters and PWM signal generators have been analog circuits. Thus, in actuator drivers, which are used for driving an optical pick-up device etc. and requiring extremely high accuracy, a sufficient design margin and a sufficient layout size have been needed to absorb process variations and temperature variations. Furthermore, a compensation circuit has been required. Since the signal bandwidth is low, there is a need to increase the element constant of a phase compensation filter. An external resistive element and an external capacitive element are needed. Therefore, the area and power consumption are difficult to reduce.
As digitalization of recent control of optical disks progresses, torque command signals output from controllers are also being digitalized. However, since actuator drivers are in analog form, the digital torque command signals need to be converted to analog signals using a D/A converter. As described above, optical disk devices control various control targets, and a plurality of torque command signals are present. Accordingly, the same number of D/A converters are required. In the actuators requiring the accuracy of 10 bits or more, D/A converters need considerable large power consumption. The circuit scale and power consumption are assumed to further increase in the future.
Full digitalization of actuator drivers is suggested to address the drawback of the analog form. For example, a fully digitally controlled actuator driver detects a current flowing through a load using a sense resistor, converts a detection signal from analog to digital, and feeds back the converted detection signal to perform phase compensation of a torque command signal in the digital region, thereby PWM-driving the load.
In a conventional fully digitally controlled actuator driver, thermal noise generated in a sense resistor may deteriorate the control accuracy. Therefore, there is a need for a fully digitally controlled actuator driver, which performs highly accurate operation without using any sense resistor.